1. Field of the Invention
This invention relates to single lens reflex cameras having electromagnetic drive sources with an electromagnetic force driving directly the focal plane shutter to move.
2. Description of the Prior Art
The conventional cameras have generally made use of a spring or mechanical drive power source in moving the shutter. It is also the common practice in the prior art that such spring power not only is used as the drive force of the shutter, but also is made to serve as a power for initiating a returning movement of the mirror and automatic diaphragm and a releasing of the film transporting mechanism from the locking connection.
Recently a great advance has been achieved in the electronization and compactness of cameras which permits the exposure control and the sequence control operation to be performed electronically. However, even in such highly electronized camera, the drive power source for the shutter is constructed likewise as has been mentioned above, in the mechanical form, thus leading to make the camera structure complicated and to hinder a further minimization of the bulk and size of the camera.
On this account, it is recently proposed to provide for the camera with an electromagnetically driven shutter in which the operation of the shutter is performed directly by the electromagnetic force.
Since this type camera operates under the action of an electromagnetic force of the electronically operated magnetic control device, as that electromagnetic force F may be expressed by F=BIL, being proportional to the flux density B, current intensity I and coil length L, in order to drive the shutter to move by an increased driving power, therefore, at least one of the factors B, I and L must be increased. However, the flux density obtained by the magnetic material available at the present time has a limit, and the current intensity available from the battery accommodated in the camera housing has also a limit. Further as for the coil length, upon consideration of its incorporation in the camera, it cannot be made so much long. For these reasons, the electromagnetic force for driving the shutter blades is necessarily limited to a certain lower value than is desired.
Therefore, in the camera provided with the electromagnetically driven shutter, the limitation of the driving power available from the electronically operated magnetic control device to a value not more than to assure the operation of the shutter with sufficient reliability tends to unstabilize the camera operation when the driving power is used up in part to actuate a returning operation of the mirror and automatic diaphragm and to release the film transporting mechanism from the locking connection.
An object of the present invention is to eliminate the above-described drawbacks and to provide a camera with an electromagnetic drive source producing an output power all of which is exclusively used as the driving torque of the shutter, while as the driving force necessary to actuate an initiation of returning movement of the mirror and automatic diaphragm and of releasing of the film transporting mechanism from the locking connection, use is made of an electromagnetic device, whereby the operation of said electromagnetic device is controlled by a deactuating signal for the shutter.
This and other objects of the present invention will become apparent from the following description of an embodiment thereof.